There are many different purposes of measuring the absolute temperature. Within a particular sub-area of this technical field there is a need for performing the measurement at a very high resolution. A resolution of a ten thousandth of a degree Celsius or better is required in many applications. The present invention relates to such high resolution measurements. One example thereof is absolute temperature measurements in calorimetry. When executing calorimetric measurements and other measurements demanding high accuracy measurement and control of the temperature, there exist different problems associated with various circumstances of measurement. In cases where a rather wide range of temperatures is scanned it is necessary that the measurement apparatus provides for a large continuous dynamic range.
Swedish patent No. 8602265-4, to Jaak Suurkuusk, discloses an apparatus for measuring the absolute temperature of a measurement body at a high resolution. This prior art apparatus is capable of providing a high resolution over a wide range, and it works well for temperature scanning applications. The resolution is at least 10−5K. The good performance of the Suurkuusk apparatus is obtained primarily due to an employment of a relative temperature measurement between the measurement body and a reference body. By obtaining knowledge of an initial absolute temperature of the measurement body, the following relative temperature measurements during the scanning provides for the high resolution estimate of the absolute temperature of the measurement body. Unfortunately this prior art method has proven not to be optimised for isothermal conditions, such as, for example, in a calorimeter wherein the temperature of a liquid is to be kept at a constant temperature over several days or more. The same applies for slow scannings. The problem is a minor offset caused by non-ideal amplifier electronics. The offset causes a drift of the measured temperature.
However, for isothermal applications typically a direct absolute temperature measuring thermometer, such as a resistance thermometer, for example a platinum resistance thermometer or a quarts thermometer, has been used. Those thermometers are good as regards long term stability. However, a problem of those known thermometers measuring the absolute temperature directly is a limited resolution, at the best about 10−5K, which for many possible applications is not good enough.